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Sen. John McCain, R-Ariz. may have cut into Democratic presidential rival Barack Obama's poll lead because of the Russia-Georgia conflict, negative ads and the public's concern about Obama as commander-in-chief.

WASHINGTON — With just days before the vice-presidential announcements, the political conventions and the final sprint to Election Day, Republican Sen. John McCain has cut Democrat Sen. Barack Obama’s national lead in half, according to the latest NBC News/Wall Street Journal poll.

“Whatever momentum that Obama took into the summer, he really appears to have lost it,” says Republican pollster Neil Newhouse, who conducted the survey with Democratic pollster Peter D. Hart. “It is not a dead heat, but it is close.”

The survey also shows that both presidential candidates face their share of challenges. For Obama, he receives the support of just one in two voters who backed Hillary Clinton in the primaries, and he trails his Republican rival on handling terrorism, the war in Iraq and international crises like the recent conflict between Russia and Georgia.

As for McCain, nearly eight in 10 voters believe that the Arizona senator would closely follow President Bush’s policies if elected, and respondents view him as the weaker candidate on the issues of the economy and health care — which rank among the public’s top concerns in the poll.

Overall, Obama holds a three-point lead over McCain, 45-42 percent, which is within the survey’s margin of error. That’s down from Obama’s six-point advantage last month, 47-41 percent.

The tightening race Hart lists three reasons. First, the conflict in Georgia as well as the Olympics have moved the news focus from the economy to foreign affairs, terrain that McCain finds more comfortable. Indeed, the poll shows McCain holding advantages over Obama in handling terrorism (51 to 23 percent), international crises (52 to 27 percent) and the war in Iraq (46 to 36 percent).

By comparison, Obama leads on health care (48 to 27 percent), the environment and global warming (47 to 21 percent), jobs and unemployment (47 to 25 percent), and improving the economy (42 to 30 percent).

Second, Hart explains that McCain’s barrage of negative TV ads against Obama — which began after the Democrat’s highly publicized overseas trip — seems to have worked so far. (Yet according to the poll, 29 percent believe McCain has been running a negative campaign, compared with just 5 percent who say that about Obama.)

And third, there are still doubts about Obama’s ability to be commander-in-chief. In the poll, 50 percent say they have confidence in McCain in that position. But just 39 percent say the same of the Illinois senator.

The Clinton factor Yet perhaps the biggest factor keeping the presidential race close has been Obama’s inability to close the deal with some of Hillary Clinton’s supporters. According to the poll, 52 percent of them say they will vote for Obama, but 21 percent are backing McCain, with an additional 27 percent who are undecided or want to vote for someone else.

What’s more, those who backed Clinton in the primaries — but aren’t supporting Obama right now — tend to view McCain in a better light than Obama and have more confidence in McCain’s ability to be commander-in-chief.

For these reasons, Hart believes that Clinton’s speech on the Tuesday night of the Democratic convention will be a significant event. “The Democratic convention is more than a coronation,” he says. “It is an event where the words of Hillary Clinton are probably going to be exceptionally important.”

Hart adds, “The Hillary Clinton campaign may be over, but the Clinton factor remains an important part of the election.”

It’s also worth noting that while Obama leads McCain by three points in the poll, Clinton edges the Republican by six points in a hypothetical match up, 49 to 43 percent. But she remains a polarizing figure: 49 percent say they don’t want to see her as president someday, and 42 percent view her favorably versus 41 percent who see her in a negative light.

McCain’s challenges Although McCain has cut into Obama’s poll lead, the Arizona senator faces some steep challenges that his campaign has yet to fully address. For starters, 77 percent of respondents believe that McCain — if elected — would closely follow the policies of President Bush, whose approval rating remains mired in the low 30s.

Strikingly, the number believing this about McCain is unchanged since March. Newhouse, the GOP pollster, says that if one of the McCain campaign’s goals this summer was to create some distance from Bush, “that wasn’t achieved.”

In addition, November is still shaping up to be a change election. A whopping 60 percent say it’s time to have a president who will focus on progress and moving America forward, compared with 35 percent who would rather have a president who focuses on protecting what has made America great.

Also in the poll — which was conducted of 1,005 registered voters from Aug. 15-18, and which has an overall margin of error of plus-minus 3.1 percentage points — just 18 percent think the country is headed in the right direction.

Focusing on the economy also underscored the theme of another poll, where voters said neither candidate had identified what he would do as president, according to the latest New York Times/CBS News poll. Voters also stressed that both candidates needed to use their conventions to give Americans a better sense of their plans with the faltering economy, high energy costs, health care and national security.

For next week’s Democratic convention to be a success, Hart says that not only does Hillary Clinton have to make the case to her supporters that Obama is the right choice for president, but Obama and the Democrats must expose McCain’s record and his ties to Bush.

“If McCain continues to be on the offensive and the Obama people do not put out the McCain record, that will be a huge mistake.”